Alloys



1962 w. P. FENTIMAN ETAL 3,049,425

ALLOYS Filed Nov. 12, 1959 9 v V rwA/mmx o I 2 D 3 F 4c 1, ALUMINIUM INVENTORS: William Percival Fenfiman, Sfuar? Leslie Ames, Pefer Harlow Morfon, Harry Wi/fr'd Mead,

WWW/M4 A TTORNEYS.

United States. Patent 3,049,425 I ALLOYS William Percival Fentiman, Birmingham, England, Stuart Leslie Ames, Natrona Heights, Pa., and Peter Hariow Morton and Harry Wilfrid Mead, Birmingham, England, assignors to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed Nov. 12, 1959, Ser. No. 852,493 Claims priority, application Great Britain Nov. 14, 1958 10 Claims. (Cl. 75-1755) This invention is concerned with titanium-base alloys which have high temperature creep strength and which do not undergo embrittlement during use at high temperature.

Alloys for use in certain elevated temperature applications where dimensional stability is important, such as gas turbine compressor blades, require to have good creep properties, together with adequate strength and freedom from embrittlement during service. It is desirable that an alloy for use in such applications should possess as many as possible of the following properties: high room temperature ultimate strength and adequate ductility, high strength and low creep rates at temperatures of 400 C.

. or more, freedom from embrittlement, high tolerance for hydrogen, good forgeability, low density and good oxidation resistance.

Throughout this specification the proportions of all components are specified in terms of percent by weight.

Titanium-base alloys have been proposed for such applications since they have moderately low density and good oxidation resistance and certain alloys have good properties at elevated temperatures. One such alloy is that containing 13% tin and 2.75% aluminium which has good creep properties but suffers from the disadvantage that at certain levels of hydrogen content serious embrittlement at service temperatures is encountered which has rendered the alloy unsuitable for use in the above-mentioned applications unless it is Vacuum annealed to reduce the hydrogen content. This is an expensive process and obviously adds to the cost of production.

We have found that by modifying the composition of titanium-tin-aluminium alloys good creep resistance without embrittlementat all levels of hydrogen content can be obtained when the alloys have been heat-treated.

An object of the invention is to provide titanium-base alloys having good creep properties. Another object of the invention is to provide titanium-base alloys with good creep properties which do not undergo embrittlement during use at high temperatures.

A further object is a titanium-tin-aluminium alloy having good tolerance for hydrogen the properties of which can be raised to higher levels by addition elements. A still further object is a heat-treatment which, with modifications, can be applied to the alloys of the invention to produce creep properties of a high order.

Other objects and advantages of the invention will become apparent from the detailed description thereof.

Titanium-base alloys having good creep properties which are free from embrittlement at elevated temperatures consist essentially of tin and aluminium, the tin content and the aluminium content relative to that tin content being in the range 14% tin with 0.5% aluminium, 14% tin with 2.2% aluminium, 7% tin with 4.25% aluminium and 7% tin with 2.5% aluminium and -0.5 silicon balance titanium and usual impurities.

let:

A desirable range of composition is that in which' the tin and aluminium contents are between the following limits: 13% tin with 1% aluminium, 13% tin -with 2.5 aluminium, 9% tin with 2% aluminium, 9% tin with 3.6% aluminium and 00.5% silicon. The preferred range of composition is that in which the tin and aluminium contents are between the following limits: 12% tin with 1.75% aluminium, 12% tin with 2.75% alu minium, 10% tin with 2.75% aluminium and 10% tin with 1.75 aluminium and 00.5% silicon. The ranges of composition of tin and aluminium content are illustrated in the accompanying drawing in which:

Point A represents 14% tin, 0.5% aluminium, Point B represents 14% tin, 2.2% aluminium, Point C represents 7% tin, 4;25% aluminium, Point D represents 7% tin, 2.5 aluminium, Point L represents 13% tin, 1% aluminium, Point M represents 13% tin, 2.5 aluminium, Point N represents 9% tin, 3.6% aluminium, Point 0 represents 9% tin, 2% aluminium, Point P represents 12% tin, 1.75 aluminium, Point Q represents 12% tin, 2.75% aluminium, Point R represents 10% tin, 2.75% aluminium and Point S represents 10% tin, 1.75 aluminium.

The usual impurities found in titanium-base alloys include carbon, oxygen, nitrogen, hydrogen and'iron and it is desirable that the amounts of such elements should be kept as low as possible.

In the following description relating to various compositions of alloys, in many instances no reference is made to the titanium content, but it is to be understood that the remainder of the composition is titanium and'usual impurities. In the description and tables the expression El. percent on 4 /K refers to the gauge length of the test piece and means the elongation percent .on 4 times the square root of the cross-sectional area. i

The line BC of the figure represents the limit of composition of alloys having elongation values ,of not less than 10% on 4 /A with a hydrogen content of up to parts per million, determined on specimens heat t-reated 30 minutes at 1100 C. air cooled, reheated to 800 C. and furnace cooled. Alloys having compositions on the left of the line BC have at all commercial hydrogen levels been found to be free from embrittlement after heattreating to produce the best creep properties. On the right of the line, the amount of hydrogen present in the alloy afiects the tendency to become embrittled and the further the composition from the line the smaller is the amount of hydrogen that can be tolerated.

This decrease in the tolerable hydrogen content with increasing alloy content is rapid and the line XY represents the limit of composition of alloys having elongation values of not less than 10% when the hydrogen content does not exceed 10 parts per million. It will be seen that the difference in composition between alloys on the limit BC and alloys on the limit XY is small and is equivalent to about 1.5% of aluminium.

Alloys in accordance with the invention are limited to a small area on the left of the line BC andalloy composicompositions fall within the area. Thus, whilst certain of the alloys outside the area may have, for example, good ductility, they may be rather weak or have poor forgeability or, on the other hand, they may have good tensile strength but rather high creep rate or may suffer embrittlement.

We have found that the best creep properties in the alpha-type ternary titanium-tin-aluminium alloys in accordance with the invention are associated with an acicular type of structure and such a structure may be produced by heat-treatments. The alloys are heated to a temperature in the beta field, cooled and reheated in the upper part of the alpha field, the rate of cooling from the beta field determining the properties. Slow cooling, as by air cooling gives a low creep rate at 500 C. whilst fast cooling as by quenching into water gives a stronger material with a moderately higher creep rate. A heat-treatment which has been found to give satisfactory results is to heat the alloy to a temperature of 1100 C., air cool or quench to room temperature and reheat to 700 or 800 C. for a period and air cool or cool in the furnace to room temperature. When air cooled, the alloy is allowed to cool at a natural rate in free air and when furnace cooled the alloy cools at the rate at which the furnace cools when closed and the heating source turned Table I shows the tensile properties of a number of titanium-tinaluminium alloys outside the range of alloys in accordance with the invention. All the examples contained about 180 parts per million of hydrogen and had been heated to 1100 C. for 30 minutes and air cooled and then reheated to 800 C. for 1 hour and furnace cooled. The elongation of most of the alloys is below which is the minimum acceptable ductility value. Of those alloys which have acceptable elongation figures the majority have lower strength than the alloys of the invention.

In Table II are given the tensile properties of alloys which fall within the range of composition in accordance with the invention and of alloys which are near that range and which have been treated and tested in the same manner as those in Table II. It will be seen that there is a marked tall in ductility of alloys which are on the right of the line BC of the figure, these alloys being outside the range. The strength and ductility of all of the alloys falling Within the range are good. Creep strength is related to the total content of tin and aluminium and those alloys at the lower end of the range have lower creep strength than those at the upper end. In general, alloys containing less than8% tin have more limited applications than those containing more than 8% tin but ductility is good, e.g. an alloy containing 7.7% tin and 3.1% aluminium has, after heat-treatment, elongation and 23% reduction in area values.

The area LMNO of the figure represents compositions in which a total plastic strain of about 0.1% or less is produced when creep tested at 400 C. under a stress of 25 tons/ sq. inch over a period of 300 hours after quenching from 1100 C. and annealing at 800 C. followed by air cooling. Table III shows the total plastic strain values obtained from alloys which fall within the area. Of the compositions which fall within the area LMNO of the figure, the best combination of properties is found in the alloy containing 11% tin and 2.25% aluminium. This alloy has good creep properties and is free from the occurrence of embrittlement during service. Whilst the creep properties of this alloy are not quite as good as alloys containing higher percentages of tin and aluminium, such as the 13% tin, 2.75% aluminium alloy, the ductility of the 11% tin, 2.25% aluminium during service is a considerable improvement on the known alloys. The tendency to become CIIlJbIliild in service can be determined by carrying out tensile tests on heat-treated specimens which have been subjected to creep testing. In 13a determination the ductility of the 13% tin, 2.75

, 4 in area values fell to about 7% in each case Whereas, in the case of the 11% tin, 2.25% aluminium alloy, the elongation and reduction in area values did not fall below 13% and 27% respectively at similar levels of hydrogen content.

For production purposes a suitable range of composition for the 11% tin, 2.25% aluminium alloy is 10.5% to 11.5% tin and 2%2.5% aluminium.

In the figure the line -FG marks the limit of good forgeability at 1000 C. Compositions on the left of the line have good forgeability and such compositions include almost all the alloys of the invention. Alloys on the right of the line are forgeable but rather more care is required than with alloys on the left.

It will be evident from the foregoing consideration of the properties of titanium-tin-aluminium alloys in accordance with the invention that such alloys are an improvement over previously known titanium-tin-aluminium alloys in that, in the alloys of the invention, in particular the 11% tin, 2.25 aluminium alloy, are combined good tensile properties, good creep properties at a temperature of 400 0., freedom from embrittlement, high tolerance for hydrogen, good forgeability, good oxidation resistance and moderate density. It will also be evident that all such properties are not found in all titanium-tin-aluminium alloys but an excellent combination of all or most of these desirable properties is found in the comparatively small range of composition represented by the alloys of the invention.

The creep properties of the ternary alloys can be further improved by the addition of zirconium 110%, and molybdenum 0.5-5%, and optionally silicon 0.050.5% and copper 01-25%, of which zirconium is an alpha stabiliser and molybdenum a beta stabiliser and silicon and copper are beta stabilisers which may form metallic compounds in some conditions of beat-treatment.

Excellent creep properties have been obtained from an alloy having a nominal composition of 11% tin, 2.25

aluminium, 5% zirconium, 1% molybdenum and 0.3% silicon as hereinafter described and suitable ranges of composition are: zirconium 2.5%7.5%, and molybdenum 0.8%l.2%. On a production scale with suitable melting techniques the range of composition for zirconium may be 4%6% and for silicon 0.2%0.5%.

Silicon is an optional addition but is desirable because of its beneficial effect on tensile strength.

Because molybdenum is a beta stabilizing element, alloys of the invention which contain molybdenum are alpha plus beta type alloys.

Creep tests on the preferred ternary composition with the addition of zirconium and molybdenum separately and together show that the additions are in general particularly effective at a temperature of 400 C. in reducing total plastic strain whereas at 500 C. there is a greater amount of creep. The results of creep tests on such alloys is given in Table IV, the heat-treatment being 1 hour at 1100 C., air cooled and reheated 1 hour at 700 C. and furnace cooled.

The creep properties of alpha plus beta type alloys in accordance with the invention are associated with certain types of structure. An acicular type of structure produced by solution treatment at 1100 C. and ageing at 700 C. with appropriate cooling rates gives low creep rates and an equiaxed structure, produced at lower temperatures, results in greater ductility but increased creep. Examples of the effects of two types of heat-treatment on structure and on creep properties are given in Table V, the creep tests being carried out at 400 C. under a load of 35 tons/sq. in. for 300 hours.

Further improvements in creep properties of an alpha plus beta type alloy of nominal composition 11% tin, 2.25 aluminium, 5% zirconium, 1% molybdenum may be brought about by the addition of 0.05% to 0.5% of silicon to the alloy. There is a progressive reduction in 1 y as shown by elongation and reduction initial plastic strain up to 0.2% silicon at which composi- Reduction in area percent Reduction in area, percent El. percent on El. percent on 4 /A TABLE I U.T.S., t./in.

237024 8 56074404 07105931451 3544 65M3flM 5553400-OQ0356555066 TABLE II It is an important feature of the in- 000222254055477777m99ummmn m tion the initial plastic strain has disappeared. Strength is addition elements raise the levels of the properties of the good and the alloys are free from embrittlement. Bebase but do not remove the embrittlement charactertween 0.20% and 0.5% silicon, properties do not change istics of a base which is inherently of low ductility under appreciably but above 0.5 silicon there is a tendency tocreep conditions. wards inhomogeneity and embrittlement. The composivention that by selecting appropriate compositions an tion, 11% tin, 2.25% aluminium, 5% zirconium, 1% alloy may be produced having the optimum properties molybdenum, 0.3% silicon is a particularly useful alloy for the particular application envisaged having regard to for elevated temperature applications in which the rethe service temperature and stress involved. Thus it is quirements are not greater than 0.1% total plastic strain now possible to meet a requirement of 0.1% total plastic at 400 C. under a load of 35 tons (78,400 pounds)/sq. strain at 400 C. in 100 hours at a load of 78,400 pounds/ in. for 100 hours. The efiect of different silicon consq. in. with a titanium-base alloy without embrittlement tents on creep properties as described above is shown in and this represents a very considerable improvement on Table VI in which the heat-treatment given to the specititanium-base alloys hitherto known. mens was 1 hour at 900 C., cooled, reheated at 500 C. for 24 hours and air cooled. Creep tests were carried 15 g at 4000 under a load of 35 tons/Sqfor 300 Tensile Properties of Titanium-Aluminium-Tin Alloys 1 ours. a

The best heat-treatment for the 11% tin, 2.25 alu- $255, 3 25 About 180 ppm Hydrogen After Heat minium, 5% Zirconium, 1% molybdenum, 0.3% silicon alloy is that given to the specimens in Table The effects of varying the ageing temperature on creep properties of the alloy are given in Table VII in which it will be seen that, for the same creep conditions as in Table VI, increasing the ageing temperature increases the total plastic strain and reduces strength after creep tests, whilst there is also some loss of ductility.

The 11% tin, 2.25% aluminium, 5% zirconium, 1% molybdenum, 0.3% silicon alloy may be heated to temperatures above the beta transus of 950 C. Without suffering embrittlement and this is shown in Table VIII, in which the specimens, after heating to various temperatures in the beta field, have been solution treated at 900 C. and aged at 500 C. This particular alloy can be forged in the beta field without fear of subsequent embri-ttlement and without having to adopt complex forging schedules to avoid embrittlement and this characteristic of the alloy is important in facilitating manufacture of such components as compressor blades and discs for. gas turbine engines.

Some typical properties of an alloy in accordance with 40 the invention are compared in Table IX with alloys containing molybdenum only, the alloys being in the solution treated and aged condition as previously described. When, in the fabrication or treatment of alpha-type and alpha plus beta-type alloys, it is necessary to heat them into the beta field, there is in certain cases a loss of ductility particularly when measured by reduction in area Tensile Praperfl'es Tilflnium-Tin-Aluminium Alloylf and the alloys may haveacoarse-grained fracture. Whilst Containing About 180 ppm Hydrogen After Healthe ductility can be restored by working the alloys in the T retliment alpha plus beta field by considerable amounts, serious loss of ductility can be avoided by the addition of boron to the alloy.

Boron can also be used to increase the strength of the alloys without loss in ductility and to reduce the total plastic strain under creep conditions particularly at tem- 55 peratures around 400 C. Improvements in creep prop- :erties and strength resulting from addition of boron are illustrated in the results set out in Table X in which specimens were heat-treated by air cooling from 1100 'C., reheated to 700 C. and furnace cooled. The range over which boron additions are elfective in this respect is from 0.005 to 0.5% preferably 0.005% to 0.2%. The actual amount to be added depends upon the particular alloy but additions of the order of 0.025% have been found to be advantageous in many alloys. Alloys of the 65 present invention may, therefore, be modified by the addi- 'tion of boron within the above-mentioned ranges in order to avoid serious loss of ductility on heating into the beta field. This is of importance in permitting forging to be carried out in the beta field without impairing ductility seriously. i

The outstanding creep properties described above depend in the first place on a titanium-tin-aluminium base which at all commercial hydrogen contents has good prop- ,erties and is inherently free from embrittlement.

The

ABLE III Creep Properties of Ti-Sn-Al Alloys at 400 C. at 25 T ons/Sq. In. for 300 Hours Heat Treated Total Plastic Strain, percent PFPPPPPP cnooooormcmwtDvbmC Quomoow-a:

TABLE IV 3 TABLE v11 Effect of Varying Ageing Temperature on in. at 400 C.) and Tensile Properties 11% Sn, 2%% Al, Zr, 1% M0, 0.3% Si.

Creep (35Tons/ Creep Properties at 400 C. and 500 C of Ti, 11% Sn, 2% Al Containing M0 and Zr Heat Treated Tensile Properties after Creep Percent 0.01% Testing Total Plas- Proof Composition Test Conditions tic Strain Stress at in 300 Test Percent Percent hours Tertnpera- EL on Rtedueure in. ion

4 i/K Area 11S11+2%Al+5Zr 35 torgsgn. at 2.196 21. 8 60. 5 14 15 400 11Sn+234Al+10Zr 0.200 31. 2 68. 4 1O 12 11Sn+2MAl+2Mo 0. 415 30. 1 66. 5 8 10 11Sn+2%Al+5Zr+} M0 0. 234 27. 7 62. 4 12 15 11Sn+2%Al+5Zr+1Mo- 0. 096 35 68.9 9 10 11S +2%Al+5Zr 0. 049 15 62. 2 15 23 11SI1+2$4A1+10Zr 0.080 15 1 65.0 15 19 11Sn+254Al+2Mo 0. 398 15 70.0 8 8 11Sn+254A1+5Zr+ Mo 0. 132 15 65. 9 7 l0 11Sn+2$4Al+5Zr+1Mo 0.202 15 69. 9 6 6 TABLE V E fleet of H eat-Treatment on Structure and Properties of Ti, 11 Sn, 2% A1 ContainingoMo and Zr Percent Tensile Properties after Creep Total Testing Plastic Composition Heat-Treatment Type of Strain at Structure 400 0. Percent Percent undegastress Ii./T.S E1. on geduieo 5 in. on n tons/in. 4 H Area.

%1h1 ur attl iggfcokair cooled Aeieular... 0. 096 68. 9 9 l0 oura urnaee coo e 1 hour at 900 0. air cooled and 24 Equiaxede. 225 67.4 20 42 hours at 500 0. air cooled. glhgur att1,1%(gCC.fair cooled arid Acicular-.. 0.415 66. 5 8 10 oure 70 urnace coo e 1 hour at 900 0. air cooled and 24 Equiazei- 0. 913 67. 4 18 38 hours at 500 0. air cooled. 11Sn+234A1+4Mo 1 hour at 900 0. air cooled and 24 Equiaxed.. 0. 385 80. 5 16 hours at 500 0. air cooled.

TABLE VIII TABLE VI Efiect of Difierent Silicon Contents on Creep Tons/ in! at 400 C) 0f11% Sn,

2%% Al, 5% Zr, 1% Mo Heat Treated 1 Hour at 900 C. Air Cooled and 24 Hours at 500 C. Air Cooled Efiect of Heating 11% Sn, 2%% Al, 5% Zr, 1% Mo, 0.35% Si at Temperatures Above Beta Transus All Specimens Heat-Treated 1 Hour at 900 C. Air Cooled and 24 Hours at 500 C. Air Cooled After Beta Treatment Tensile Properties after 0.1% Creep Testing Proof Beta Treatment 1 hour at Stres tons/in. U.T.S., Percent Percent e ma Reduction on 4 /1 in Area 64.5 71.6 15 35 950 C. air cooled 61. 8 71.3 16 40 63. 9 72. 6 19 41 000 59. 4 69. 8 17 31 1,000 0. water quenched--. 6i. 9 71. 6 15 27 1,040 G. air cooled 58. 5 70. 5 17 30 1,040 0. water quenchei--. 61.9 72. 7 11 18 11' 01 d 61.0 73.0 11 12 64. 0 75. a 11 13 1,l00 0. air cooled 60.0 71. 9 3 6 l,l00 0. Water quenched... 64. 8 74.0 4 7 Typical Properties of Three Alloys Heat-Treated 1 Hour at 900 C. Air Cooled and 24 Hours at 500 C. Air

Cooled Tensile Properties at Room Temperature Stress to Creep Test Produce 0.1% Composition Temperature, Total Plastic 0.1% Percent Percent 0. Strain in Proof U.T.S., E1. on Reduc- 300 hrs Stress t./in. 4K tion m Area Room 64. 71. 0 18 41 300 44. 0 11Sn+2%Al+5Zr+1M0-!-0.3Sl 400 37.0 450 25.0 500 13. 5 Room 75. 0 88. 0 -15 20-45 300 49. 0 11Sn+2%Al+4Mfol-O.3Sl 400 35. 0 450 13.5 500 3. 5 Room 63. 0 75.0 17 49 11 Sn+2%Al+2M0+O.3Si 400 35.0

TABLE X Efiect of Baron on Creep and Tenszle Properties of 11% Sn-l-ZMr Al+5% or 10 Zx Wzth and Wzthout M olybdenum Percent Percent Percent Composition, Percent Stress Tempera- Total U.I.S. El. Reducture, 0. Plastic t./in. on 41 tion in Strain Area 11+2%+5Zr 35 400 1. 424 62v 5 17 27 11+2%+5Zr+0.025 B- 35 400 0. 784 64. 4 18 31 11+2%+5Zr+0.05 13.. 35 400 0. 674 62. 3 18 37 11+2%+5Zr+0.10 35 400 0. 179 63. 5 35 11+2%+5Zr+0.20 B 35 400 0.300 15 32 11+2%+10Zr 35 400 0. 265 64. 2 15 20 11+2 4+10Zr+0 B 35 400 0. 2 12 66. 4 15 15 11+2%+10Zr+0 05 B 35 400 0.215 68. 5 14 24 11+2%+10Zr+0.10 B 35 400 0.186 70. 4 15 11+2%+10Zr+0.20 B--. 400 0.160 72.0 16 25 11+2%+5Zr+0.5 Mo 15 500 0.132 65. 9 7 10 11+2%+5Zr+0.5 M0+0.2 B. 15 500 0.139 68. G 16 31 11+2V;+5Zr+1.0 M0 35 400 0.096 68. 4 10 12 1l+2}4+5Zr+1.0 1\I0+0.025 B 35 400 O. 093 69. 3 13 23 All specimens heat-treated 1 hour at 1100 0. air cooled and 1 hour at 700 0. furnace cooled.

We claim:

1. Titanium-base alloys consisting essentially of tin and aluminium in the area defined by straight lines connecting the following four compositions in the ternary constitutional diagram of the titanium-tin-aluminium system: 14% tin, 0.5% aluminium; 14% tin, 2.2% aluminium; 7% tin, 4.25% aluminium; 7% tin, 2.5% aluminium, up to 0.5% silicon, 1%10% zirconium, 1%-5% molybdenum, balance titanium and usual impurities, said percentages being by weight.

2. An alloy as claimed in claim 1 containing in addition O.1%-2..5% copper by weight.

3. An alloy as claimed in claim 1 having an acicular type structure.

4. Titanium-base alloys consisting essentially of tin and aluminium in the area defined by straight lines connecting the following four compositions in the ternary constitutional diagram of the titanium-tin-aluminium system: 13 tin, 1% aluminium; 13% tin, 2.5% aluminium; 9% tin, 2% aluminium; 9% tin, 3.6% aluminium; up to 0.5% silicon; 2.5 %7.5% zirconium; 0.8%1.2% molybdenum, balance titanium and usual impurities, said percentages being by weight.

5. Titanium-base alloys consisting essentially of tin and aluminium in the area defined by straight lines connecting the following four compositions in the ternary constitu- 7. An alloy as claimed in claim 6 having an aciculartype of structure and a creep strength of not less than: 78,400 pounds per square inch at 400 C. based on a:

criterion of 0.1% creep strain in 100 hours at 400 C.

8. Titanium base alloys consisting essentially of tin and aluminium in the area defined by straight lines connecting; the following four compositions in the ternary constitu-- tional diagram of the titanium-tin-aluminium system: 14%, tin, 0.5 aluminium; 14% tin, 2.2% aluminium; 7%) tin, 4.25% aluminium; 7% tin, 2.5% aluminium; up to 0.5 silicon 1%-10% zirconium, 1%5% molybdenum, 0.005%0.5% boron, balance titanium and usual impuri-- ties, said percent-ages being by weight.

9. An alloy as claimed in claim 8 having an acicular type structure.

10. A method of heat treating a titanium-base alloy consisting essentially of, by weight, 10.5%11.5% tin, 2.0%2.5% aluminium, 4%6% zirconium, 0.8%1.2% molybdenum, 0.1%-0.5% silicon, balance titanium and usual impurities which comprises solution heat treating the alloy at 900 0, air cooling, aging the alloy at 500 C. and air cooling, whereby the creep strength of not less than 78,400 pounds per square inch at 400 C., based on a criterion of 0.1% creep strain in 100 hours at 400 C.

References Cited in the file of this patent UNITED STATES PATENTS Jafiee et a1. Feb. 16, 1954 Jaffee et al Jan. 29, 1957 Jatfee et a1 July 2, 1957 Jaffee et a1 Jan. 6, 1959 FOREIGN PATENTS Australia May 16, 1957 

1. TITANIUM-BASE ALLOYS CONSISTING ESSENTIALLY OF TIN AND ALUMINUM IN THE AREA DEFINED BY STRAIGHT LINES CONNECTING THE FOLLOWING FOUR COMPOSITIONS IN THE TERNARY CONSTITUTIONAL DIAGRAM OF THE TITANIUM-TIN-ALUMINUM SYSTEM: 14% TIN, 0.5% ALUMINUM; 14% TIN, 2.2% ALUMIMIUM; 7% TIN, 4.25% ALUMINUM; 7% TIN, 2.5% ALUMINIUM, UP TO 0.5% SILICON, 1%-10% ZIRCONIUM, 1%-5% MOLYBDENUM, BALANCE TITANIUM AND USUAL IMPURITIES, SAID PERCENTAGES BEING BY WEIGHT. 